The present invention relates to a safety switch for generating an enable signal as a function of the position of a moveable guard door, and more particularly to a safety switch of this kind having a locking element designed to lock the guard door in the closed position.
Safety switches of this kind may also be referred to as interlock devices with guard locking. They are used on guard doors, guard flaps or the like, which are intended to prevent access to an automated machine or system as long as the machine or system is in a hazardous state. The machine may be, for example, a robot, a machine tool having a rapidly rotating spindle, a transportation or conveying system, a press or another machine or system whose operation represents a hazard to people located in the working area of the machine. The safety switches can be used as signaling devices, by means of which a control device can identify the closed state of the guard door. The control device is typically configured to bring the machine into operation only when the guard door is closed. If the guard door is opened during running operation (if possible), the control device needs to bring the machine or system into a nonhazardous state by, for example, switching off the power supply to the machine or system.
There is a large number of machines and systems which represent a hazard for a certain amount of time even after they have been shut down, for example because the machine or system is still running down. For such application cases, safety switches are required which prevent the guard door from being opened until the machine or system has reached its nonhazardous state. This function is here referred to as guard locking.
Conventionally, the prior art safety switches have what is called an activator, which is arranged on the moveable guard door. When the guard door is closed, the activator engages in an activator receptacle on the door frame, which is detected by means of one or more sensors. In the case of a safety switch with guard locking, the activator is also locked in the activator receptacle preventing it from being withdrawn. The activator in this case fulfills two functions, namely firstly that of a detector element, by means of which the closed position of the guard door can be detected, and secondly that of a bolt, which prevents the guard door from being opened as long as the activator is locked in the activator receptacle. The activator can be enabled, for example, via an electromotive actuator, which is activated by the control device as soon as the monitored machine or system has assumed its safe state.
One example of such a safety switch is disclosed by DE 43 28 297 C1. The activator (referred to as a key therein) is a flat metal plate having a central opening, in which a cam can engage in order to realize the guard locking function. The activator receptacle is a narrow channel, whose internal dimensions are only slightly greater than the external dimensions of the activator. The known safety switch therefore has the disadvantage that the guard door and the frame need to be aligned very precisely with respect to one another so that the activator can engage in the activator receptacle. It is thus difficult to install this known safety switch. Problems also result if the guard door drops over the course of time, with the result that the installation tolerances are no longer maintained. In this case, the guard door can no longer be closed properly.
DE 196 24 172 C2 discloses another safety switch, where the activator needs to be inserted into a narrow activator receptacle. This known safety switch also requires tight installation tolerances.
WO 00/64054 describes various embodiments of prior art safety switches, but the mechanical design is only illustrated schematically. A characterizing feature of these known safety switches is the fact that the activator and the activator receptacle each have signal means, which are arranged such that signal interchange is only possible in the case of a locking engagement. The advantage of this implementation consists in the fact that only a single sensor is required in order to meet the safety-related requirements of the relevant European Standard EN 1088. The problems outlined above in connection with tight installation tolerances are not addressed in WO 00/64054.
DE 103 05 704 B3 describes a prior art safety switch which alleges to allow high installation tolerances and dropping of the guard door. The known safety switch has an activator, which can be moved between a first and a second position via a handle. In the second position, the activator protrudes so far out of the door part that it can engage in an activator receptacle on the frame part, thereby locking the guard door. Provided in the frame part is a pivotable locking element, by means of which the activator can be locked in the activator receptacle. Both the activator and the locking element have (in the normal installed position) vertically extending grooves and projections, which match one another and engage in one another in the locked state. Since the grooves and projections extend in the vertical direction, the activator and the locking element can move towards one another in the vertical direction. As a result, this known safety switch offers increased installation tolerance in the vertical direction. In the horizontal direction, the freedom of movement is limited by the depth of the grooves and projections.